Simplify code that makes hal the default json media type

See gh-25546

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/hateoas/HypermediaAutoConfiguration.java

 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -22,18 +22,21 @@ import org.springframework.boot.autoconfigure.AutoConfigureAfter;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplication;
 import org.springframework.boot.autoconfigure.data.rest.RepositoryRestMvcAutoConfiguration;
 import org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration;
 import org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration;
 import org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
+import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
-import org.springframework.context.annotation.Import;
 import org.springframework.hateoas.EntityModel;
 import org.springframework.hateoas.client.LinkDiscoverers;
 import org.springframework.hateoas.config.EnableHypermediaSupport;
 import org.springframework.hateoas.config.EnableHypermediaSupport.HypermediaType;
+import org.springframework.hateoas.mediatype.hal.HalConfiguration;
+import org.springframework.http.MediaType;
 import org.springframework.plugin.core.Plugin;
 import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter;
@@ -53,9 +56,17 @@ import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandl
 @AutoConfigureAfter({ WebMvcAutoConfiguration.class, JacksonAutoConfiguration.class,
 		HttpMessageConvertersAutoConfiguration.class, RepositoryRestMvcAutoConfiguration.class })
 @EnableConfigurationProperties(HateoasProperties.class)
-@Import(HypermediaHttpMessageConverterConfiguration.class)
 public class HypermediaAutoConfiguration {
 
+	@Bean
+	@ConditionalOnMissingBean
+	@ConditionalOnClass(name = "com.fasterxml.jackson.databind.ObjectMapper")
+	@ConditionalOnProperty(prefix = "spring.hateoas", name = "use-hal-as-default-json-media-type",
+			matchIfMissing = true)
+	HalConfiguration applicationJsonHalConfiguration() {
+		return new HalConfiguration().withMediaType(MediaType.APPLICATION_JSON);
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	@ConditionalOnMissingBean(LinkDiscoverers.class)
 	@ConditionalOnClass(ObjectMapper.class)

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/hateoas/HypermediaHttpMessageConverterConfiguration.java

 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -29,6 +29,7 @@ import org.springframework.beans.factory.config.BeanPostProcessor;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.hateoas.mediatype.hal.HalConfiguration;
 import org.springframework.hateoas.server.mvc.TypeConstrainedMappingJackson2HttpMessageConverter;
 import org.springframework.http.MediaType;
 import org.springframework.http.converter.AbstractHttpMessageConverter;
@@ -41,7 +42,9 @@ import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandl
  *
  * @author Andy Wilkinson
  * @since 1.3.0
+ * @deprecated since 2.5.0 in favor of a {@link HalConfiguration} bean
  */
+@Deprecated
 @Configuration(proxyBeanMethods = false)
 public class HypermediaHttpMessageConverterConfiguration {
 

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/hateoas/HypermediaAutoConfigurationTests.java

 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -29,15 +29,16 @@ import org.springframework.boot.test.context.FilteredClassLoader;
 import org.springframework.boot.test.context.runner.WebApplicationContextRunner;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.hateoas.MediaTypes;
+import org.springframework.hateoas.RepresentationModel;
 import org.springframework.hateoas.client.LinkDiscoverer;
 import org.springframework.hateoas.client.LinkDiscoverers;
 import org.springframework.hateoas.config.EnableHypermediaSupport;
 import org.springframework.hateoas.config.EnableHypermediaSupport.HypermediaType;
 import org.springframework.hateoas.mediatype.hal.HalLinkDiscoverer;
 import org.springframework.hateoas.server.EntityLinks;
-import org.springframework.hateoas.server.mvc.TypeConstrainedMappingJackson2HttpMessageConverter;
 import org.springframework.http.MediaType;
 import org.springframework.http.converter.HttpMessageConverter;
+import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
 import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -87,28 +88,28 @@ class HypermediaAutoConfigurationTests {
 	}
 
 	@Test
-	void supportedMediaTypesOfTypeConstrainedConvertersIsCustomized() {
+	void whenUsingTheDefaultConfigurationThenMappingJacksonConverterCanWriteHateoasTypeAsApplicationJson() {
 		this.contextRunner.run((context) -> {
 			RequestMappingHandlerAdapter handlerAdapter = context.getBean(RequestMappingHandlerAdapter.class);
-			for (HttpMessageConverter<?> converter : handlerAdapter.getMessageConverters()) {
-				if (converter instanceof TypeConstrainedMappingJackson2HttpMessageConverter) {
-					assertThat(converter.getSupportedMediaTypes()).contains(MediaType.APPLICATION_JSON,
-							MediaTypes.HAL_JSON);
-				}
-			}
+			Optional<HttpMessageConverter<?>> mappingJacksonConverter = handlerAdapter.getMessageConverters().stream()
+					.filter(MappingJackson2HttpMessageConverter.class::isInstance).findFirst();
+			assertThat(mappingJacksonConverter).isPresent().hasValueSatisfying(
+					(converter) -> assertThat(converter.canWrite(RepresentationModel.class, MediaType.APPLICATION_JSON))
+							.isTrue());
 		});
 	}
 
 	@Test
-	void customizationOfSupportedMediaTypesCanBeDisabled() {
+	void whenHalIsNotTheDefaultJsonMediaTypeThenMappingJacksonConverterCannotWriteHateoasTypeAsApplicationJson() {
 		this.contextRunner.withPropertyValues("spring.hateoas.use-hal-as-default-json-media-type:false")
 				.run((context) -> {
 					RequestMappingHandlerAdapter handlerAdapter = context.getBean(RequestMappingHandlerAdapter.class);
-					for (HttpMessageConverter<?> converter : handlerAdapter.getMessageConverters()) {
-						if (converter instanceof TypeConstrainedMappingJackson2HttpMessageConverter) {
-							assertThat(converter.getSupportedMediaTypes()).containsExactly(MediaTypes.HAL_JSON);
-						}
-					}
+					Optional<HttpMessageConverter<?>> mappingJacksonConverter = handlerAdapter.getMessageConverters()
+							.stream().filter(MappingJackson2HttpMessageConverter.class::isInstance).findFirst();
+					assertThat(mappingJacksonConverter).isPresent()
+							.hasValueSatisfying((converter) -> assertThat(
+									converter.canWrite(RepresentationModel.class, MediaType.APPLICATION_JSON))
+											.isFalse());
 				});
 	}
 

spring-boot-tests/spring-boot-smoke-tests/spring-boot-smoke-test-hateoas/src/test/java/smoketest/hateoas/SampleHateoasApplicationTests.java

 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,6 +16,8 @@
 
 package smoketest.hateoas;
 
+import java.util.Arrays;
+
 import org.junit.jupiter.api.Test;
 
 import org.springframework.beans.factory.annotation.Autowired;
@@ -38,8 +40,21 @@ class SampleHateoasApplicationTests {
 	private TestRestTemplate restTemplate;
 
 	@Test
-	void hasHalLinks() {
-		ResponseEntity<String> entity = this.restTemplate.getForEntity("/customers/1", String.class);
+	void hasHalLinksWhenAnythingIsAcceptable() {
+		HttpHeaders headers = new HttpHeaders();
+		ResponseEntity<String> entity = this.restTemplate.exchange("/customers/1", HttpMethod.GET,
+				new HttpEntity<>(headers), String.class);
+		assertThat(entity.getStatusCode()).isEqualTo(HttpStatus.OK);
+		assertThat(entity.getBody()).startsWith("{\"id\":1,\"firstName\":\"Oliver\",\"lastName\":\"Gierke\"");
+		assertThat(entity.getBody()).contains("_links\":{\"self\":{\"href\"");
+	}
+
+	@Test
+	void hasHalLinksWhenJsonIsAcceptable() {
+		HttpHeaders headers = new HttpHeaders();
+		headers.setAccept(Arrays.asList(MediaType.APPLICATION_JSON));
+		ResponseEntity<String> entity = this.restTemplate.exchange("/customers/1", HttpMethod.GET,
+				new HttpEntity<>(headers), String.class);
 		assertThat(entity.getStatusCode()).isEqualTo(HttpStatus.OK);
 		assertThat(entity.getBody()).startsWith("{\"id\":1,\"firstName\":\"Oliver\",\"lastName\":\"Gierke\"");
 		assertThat(entity.getBody()).contains("_links\":{\"self\":{\"href\"");